We sighted a road sign while visiting family over the weekend, which I thought might arouse some interest.
A sign for the 37th parallel of latitude at a spot way out in the country, 10.3km NE of Stawell in Victoria's west. I can't think why such a sign would be placed here?
So I thought I'd check how accurate it is by having a look on Google Earth. GE suggests that the 37th parallel is some 282 meters down the road! So which is more likely to be wrong?, the original surveyors or GE? I also noticed from GE that all the properties have been surveyed and fenced along lines of latitude. I'm thinking that many of the properties may have been surveyed after WW2 for the soldier resettlement program? Can anyone shed any light on this? Maybe you've seen some interesting road signs?
Two pictures attached, one of the sign, and a screen grab from GE showing the property boundaries following lines of latitude, a cross marks the position of the sign.
Its good for the tourists, But lots of them would be questioning what it is about.
Surveyors would give coordinates to the council or shire then it goes down the line from management to the poor workman, one questions how long the sign been in that position and if the poor road worker had a gps unit ( not likely ) his instructions would of been more likely go out of town a couple kilometers then 20 m past the tree and thats it we plonk it there.
A bit like chinese whispers.
Thanks Kev,
I was hoping for a rather more historic reason/answer!
But I can just picture the scenario you have suggested! A bit off the beaten track for tourists though.
The surveyed property lines suggest they have been there for many many years.
I'm not up with surveying, but I remember a few years back the company I worked for was changing to a Geocentric system from the old one (whatever that was). I noticed that there was a note with all older drawings saying that the positions given could be 200m+ out using the new system. Perhaps that's the reason for the discrepancy.
Its good for the tourists, But lots of them would be questioning what it is about.
Surveyors would give coordinates to the council or shire then it goes down the line from management to the poor workman, one questions how long the sign been in that position and if the poor road worker had a gps unit ( not likely ) his instructions would of been more likely go out of town a couple kilometers then 20 m past the tree and thats it we plonk it there.
A bit like chinese whispers.
I'd say the sign was placed using a local map that followed what was until recently the most popular map datum in Australia, AUS66. Google Earth used WGS84 as its datum, and the difference between the two varies from around 120 metres to 400ish metres, depending where in the country you are.
Also, on Google earth the aerial photos are more often than not slightly out in their positioning on the grid. You can test this locally by setting your GPS to WGS84 (if it isn't already) and taking the position of a prominent object in your yard. It's best to average this position over half an hour or so if you unit is capable of it. Now go inside and compare the lat and long from your GPS position, to the lat and long of that item in your yard as seen on Google Earth. You'll most likely find the two don't line up.
I was pretty sure it would have to do with different datum being used.
Must confess I don't have a GPS unit, and can't really understand why people spend so much money on them when all they need to do is read a map! That sort of money would buy a reasonable eyepiece!
can't really understand why people spend so much money on them when all they need to do is read a map!
Other than the toy value, I don't know why people buy these in-car navigators to drive around their own town either.
I still have the same handheld GPS that I bought in 1996. It's a Garmin 12XL, and I bought it because I used to do a lot of bush bashing on mountain bikes, alone, and in the middle of nowhere. The GPS wasn't so much for knowing where I was instantaneously, but for logging the track I took for overlaying on a map when I got home. It's a great trail mapping tool.
I can understand their use for orienteering, and true off road use in remote areas, but otherwise it's overkill.
A copy of Melways and the Vic Roads atlas is all that's needed otherwise.
But one could also say this about goto scopes!
Ducks head and runs!
I must admit I would be lost without mine. I do a lot of public viewings at schools, in areas I have never been to. I usually enter the school into the GPS, sometimes check the Melways just to get an idea of where I am going, and just drive there. It is particularly useful when coming home, I don't want to be checking out which little side street to take to get back to a main road, and in many cases I am not even familiar with the main roads. Once I get to a road I am familiar with, I usually ignore it and drive the rest of the way on my own. Without the GPS it would take a lot of time to find my way home and possibly risk an accident.
However, they are not perfect and a couple of times mine has navigated to the right street number, but wrong suburb
Quote:
Originally Posted by chrisp9au
Thanks Jason,
I was pretty sure it would have to do with different datum being used.
Must confess I don't have a GPS unit, and can't really understand why people spend so much money on them when all they need to do is read a map! That sort of money would buy a reasonable eyepiece!
